Sorry this is as designed in DNG format, not a bug. It is the responsibility of any software that uses the embedded previews in DNG format to apply the orientation.

If Adobe changed this, then all the software that correctly applies the orientation would then break.

The reason for this design is I did not want to have re-render the embedded previews every time any software changes the orientation metadata. That would make rotating DNG files in Bridge or Lightroom very slow.

Please report this bug against any software that is not applying the orientation correctly to embedded previews in DNG format.

With current Adobe code, previews created by the Adobe DNG Converter are either sRGB or Gray Gamma 2.2. But any utility that you write should NOT assume that will remain so forever in future versions of Adobe code. Non-Adobe software very well might already be using different preview color spaces. Any code that cares what color space the previews are in should parse and use the PreviewColorSpace tag, like I said in my previous message.